Poly(arylene ether)s are a class of plastics known for excellent water resistance, dimensional stability, and inherent flame retardancy, as well as high oxygen permeability and oxygen/nitrogen selectivity. Properties such as strength, stiffness, chemical resistance, and heat resistance can be tailored by blending poly(arylene ether)s with various other plastics in order to meet the requirements of a wide variety of consumer products, for example, plumbing fixtures, electrical boxes, automotive parts, and insulation for wire and cable.
Injection molding compositions including a poly(arylene ether), a rubber-modified polystyrene, and a flame retardant are commonly used to mold a variety of articles. These compositions are often explicitly characterized according to physical properties of molded test articles prepared from them, including objective metrics of stiffness (for example, flexural modulus), ductility (for example, notched Izod impact strength and tensile elongation at break), and heat resistance (for example, heat deflection temperature). Surface aesthetics are often an uncommunicated critical-to-quality metric for plastic articles prepared by injection molding. One common surface defect for injection-molded parts is known as splay, which is often described as splashes or fine lines that vary in color from the bulk of the molded part. Images of molded parts with and without splay are presented in the FIGURE. Splay is particularly a problem for molded parts with large, thin sections, such as, for example, plastic cases for the back-up batteries used in cell phone relay towers. The undesirable appearance of splay can lead to increased scrap rates and reduced productivity.
There is therefore a need for molding methods that reduce splay in the large, thin sections of articles molded from poly(arylene ether) compositions.